VIENTIANE, Laos — President Barack Obama put the long-simmering dispute in the South China Sea front and center on the agenda at a regional summit Thursday as it became clear that most of the other leaders gathered in the Laotian capital were going to let China off with a mild rebuke over its territorial expansion in the resource-rich waters.

"We will continue to work to ensure that disputes are resolved peacefully including in the South China Sea," Obama said in his opening remarks at a meeting with leaders of the 10-member Association of Southeast Asian Nations, or ASEAN.

He said an international arbitration ruling on July 12 against China was "binding" and "helped to clarify maritime rights in the region."

ASEAN will hold a separate summit later Thursday with other world powers, including China and the U.S. The summit is expected to let China off with a muted reprimand over its expansionist activities in South China Sea, according to a draft of their joint statement to be released Thursday.

The U.S. has repeatedly expressed concern over Beijing's actions in the resource-rich sea. Obama brought that up again.

Referring to the arbitration panel's ruling that invalidated China's claims, Obama said: "I realize this raises tensions but I also look forward to discussing how we can constructively move forward together to lower tensions and promote diplomacy and regional stability."

The draft of the summit statement said that ASEAN and its partners "reaffirmed the importance of maintaining peace, stability and security and freedom of navigation in and over-flight in the South China Sea."

"Several Leaders remained seriously concerned over recent developments in the South China Sea ... We stressed the importance for the parties concerned to resolve their disputes by peaceful means, in accordance with universally recognized principles of international laws," it said.

China has turned shoals and coral reefs into seven man-made islands and built airstrips capable of handling military aircraft on three of them. ASEAN leaders at their earlier summit on Tuesday expressed concern over China's island-building.

A joint statement after the Tuesday summit said it "took note of the concerns expressed by some leaders on the land reclamations and escalation of activities in the area, which have eroded trust and confidence, increased tensions and may undermine peace, security and stability in the region."

The use of the phrase "some leaders" in the two statements underscores the fundamental problem ASEAN and the wider East Asia Summit has in dealing with China — not all its members are willing to scold Beijing. Cambodia, for example, remains in China's camp, as does Laos to a large extent, preventing any robust statement from the consensus-bound ASEAN group.

U.S. officials, however, said that there were other critical elements in the ASEAN statement that China failed to block, and which amounted to a strong diplomatic rebuke of Beijing.

China pulled out all the stops to block any reference to the words "recent activities," ''serious concern," ''reclamation," ''militarization," ''loss of trust" and "need to respect legal processes," but failed as all these phrases made it into the statement, said a senior U.S. administration official, who requested anonymity to discuss diplomatic discussions.

Though Beijing recently announced a $600 million aid package to ally Cambodia, China was unable to get it to block the statement, said the official. Cambodia did however block an explicit mention of the tribunal's ruling, which the Philippines was willing to concede, the official said.

The issue of ownership of territories in the South China Sea has come to dominate ASEAN summits in recent years. China claims virtually the entire sea as its own, citing historical reasons. That has pitted it against the Philippines, Vietnam, Malaysia and Brunei, all members of ASEAN, which have overlapping claims.

The U.S. military has also expressed concern over the possibility that China might turn Scarborough into another island, something that would give Beijing's forces greater control over a swath of the South China Sea used as a passageway to the Taiwan Strait.